1. Field of the Invention
This invention relates generally to viewing down-hole conditions in a well, and more particularly concerns use of a surfactant to prevent a down-hole viewing instrument from being obscured by down-hole fluids such as oil and water.
2. Description of Related Art
Remote video camera systems incorporated in down-hole instrument probes can be particularly useful for visually examining wells. One of the more common uses is leak detection. The camera system may detect turbulence created by a leak and may identify different fluids leaking into the well bore. Particulate matter flowing out through a hole can be detected. Damaged, parted, or collapsed tubings and casings may also be detected. The severity of scale buildup in downhole tubulars, flow control devices, perforations and locking recesses in landing nipples can be seen and analyzed.
Additional uses for video camera systems include the detection of formation fractures and their orientations. Video logging provides visual images of the size and extent of such fractures. Downhole video is also useful in identifying downhole fish and can shorten the fishing job. Plugged perforations can be detected as well as the flow through those perforations while the well is flowing or while liquids or gases are injected through the perforations. Corrosion surveys can be performed with downhole video and real-time viewing with video images can identify causes for loss of production, such as sand bridges, fluid invasion or malfunctioning down-hole flow controls.
In all the above uses for down-hole video, it is important for the optical elements of such video camera systems, including windows, lens systems and lighting systems, to remain clear. A substantial amount of time can be involved in lowering the instrument into the well, raising the instrument up out of the well to clean the viewing or lighting elements of adherent fluids such as oil residing in the well which obscure the camera's view or attenuates the light output from the lighting system, and then lowering the instrument again. A video camera system that becomes fogged or obscured by crude oil will provide no useful data, and can delay operations. The presence of down-hole fluid, which can include oil, water, and gases, is common in such wells, and the video camera system is more efficient if the viewing and lighting elements of the video camera system are unobscured by such fluids for extended periods of time. As used herein, the term "optical element" is meant to not only apply to the elements through which images pass to reach the camera, but also to the clear or light transmissive domes or other components over light generating devices. The term "video camera system" is meant to include not only the video camera, lens, and any other optical elements for image development such as a port window, but also the lighting equipment used to illuminate down-hole subject matter.
One particularly troublesome situation involves strata of fluids in a well. Where images of the well below a stratum of crude oil are desired, it may be effectively impossible to place a clear instrument in position. Each time the instrument passes the oil layer, the exposed optical and lighting elements may become obscured by oil adhering to the optical elements. Removing the instrument to clean it will have little effect, because the instrument must pass through the same stratum after reinsertion.
Detergents, phosphates, petroleum-based coatings, acidified ethanol/isopropanol polish, and wetting agents have been used to inhibit condensation on the lens of a real-time down-hole video instrument. Various anti-fogging compositions effective for inhibiting condensation of moisture on a surface are known, including hydroaromatic alcohols, amphoteric surface active agents, silicone, linear fatty alcohol ether sulfates, hydrocarbon waxes and hydrophilic resin coatings, which have been used for inhibiting condensation of moisture on visors, windshields, and the like. However, it has been found that these coatings do not remain on the optical elements of a down-hole instrument in a sufficient amount long enough to be effective to prevent the optical elements from being obscured by oil and other well fluids under the severe environment of high temperature, pressure, and caustic fluids that can exist in a well. The harsh conditions within a well can involve hydrostatic well pressures in excess of 4.2.times.10.sup.6 kilograms per square meter (6,000 pounds per square inch) and ambient wall temperatures of 110.degree. C. (230.degree. F.) and higher. Some wells contain hydrogen sulfide gas which can have a deleterious effect on an instrument probe. It would be desirable to provide a system for producing images of down-hole conditions over an extended period of time and not have that system rendered inoperative due to the adherence of obscuring down-hole fluids or the action of caustic fluids. Coating the optical elements of a down-hole video instrument with a surfactant that would repel crude oil, inhibit condensation of moisture, and keep the optical elements of such a down-hole video system unobscured by such fluids is desirable.
However, another factor to be considered in protecting the optical elements of a down-hole viewing instrument that are exposed to down-hole fluids is the possibility that a compound applied to the surface of an optical element as a surfactant could mar, etch and essentially destroy the surface of the optical element or degrade sealing material around such an optical element under the high pressure, high temperature conditions found at great depths in well bores. Degrading the sealing material can have a disastrous effect in that the high pressure fluids may enter the instrument and render electrical circuits inoperative and cause other damage. It would be desirable that application of such a surfactant compound should not only protect the optical element to which it is applied from down-hole fluids, but also not be injurious to the surface or seal of the optical element at high temperatures and pressures. The invention meets these needs.